This invention relates to ground-based aircraft landing systems and especially to a method and means for determining the crab angle of a landing aircraft just prior to touch-down.
Ground control approach (GCA) aircraft landing systems employ radar to guide an aircraft to a point about four seconds from touch-down. At this point the radar loses altitude information because the radar cannot resolve the aircraft from its image in the ground. The landing systems also lack information about aircraft orientation with respect to the direction of the runway so that they cannot properly flare or decrab the aircraft prior to touch-down and therefore must limit landings to low crosswind conditions. A system which can determine crab angle a few seconds before touch-down so that the aircraft can be informed how much to change course to come in straight along the runway would provide a distinct improvement over present GCA systems.